1. Field of the Invention
The present invention relates to a novel photochromic azaporphyrin compound and an optical recording material using it. More particularly, the present invention relates to a novel photochromic azoporphyrin compound which is useful as the substance in various recording or memory materials, photocopying materials, light controlling materials, photosensitive printing materials, laser beam sensitive materials, photoprinting or optical filters, masking materials, actinometers or display materials.
Further, the present invention relates to an optical recording material, wherein information recording can be made by irradiation with light to change the color of a substance contained in the recording layer, and reproduction of the recorded information can be made by reading the difference in the absorbance or the reflectivity between the portion where such a color change has occured and the portion where no such color change has taken place.
2. Discussion of the Background
Various compounds have been known which have photochromic properties and which undergo coloring or discoloring when irradiated with light. Photochromic materials utilizing such properties have been proposed.
For instance, Japanese Unexamined Patent Publication No. 149812/1980 discloses a photochromic material having a spiropyrane compound of the following formula dispersed in a nitrocellulose resin: ##STR2## wherein R.sup.a is a hydrogen atom or a halogen atom, R.sup.b is an alkyl group, and R.sup.c is a hydrogen atom or an alkoxy group.
Further, Japanese Examined Patent Publication No. 28892/1970 discloses a photochromic material containing a spironaphthooxazine compound of the formula: ##STR3## wherein R.sup.d is a hydrogen atom, a halogen atom, a cyano group or an alkyl or alkoxy group having from 1 to 8 carbon atoms.
Meantime, there have been active researches in recent years to employ such photochromic compounds as the substance in reversible optical recording materials. For this purpose, the following conditions are required to be satisfied.
(1) Sensitivity to a semiconductor laser beam
(2) Non-destractive reading out property
(3) Thermal stability of recorded information
(4) Quick response
(5) Durability against repeated operation
A photochromic material containing a spirobenzopyrane derivative having a benzothiophyrane ring of the following formula has been proposed as a compound having an improved sensitivity to a semiconductor laser beam under item (1) among the above requirements. (Nobutoshi Asai et al., Collection of preliminary papers for the spring meeting of the Association of Applied Physics, p. 442 (1986)) ##STR4##
The present inventors have previously proposed in Japanese Unexamined Patent Publication No. 280264/1987 a dithienyldicyanoethene derivative of the following formula which exhibits photochromism, as a compound having an improved thermal stability of recorded information as required under item (3) and an optical recording material using the dithienyldicyanoethene derivative having excellent thermal stability of recorded information. ##STR5## wherein each of R.sup.g, R.sup.h, R.sup.i, R.sup.j, R.sup.k and R.sup.l is an alkyl group.
When a photochromic compound is used in an optical recording material, it is important that it has both the thermal stability of recorded information as required under item (3) and the sensitivity to a semiconductor laser beam as required under item (1). However, no optical recording material satisfying both of these requirements have been proposed. The optical recording material containing the above-mentioned spirobenzopyrane derivative is inferior in the thermal stability of recorded information as required under item (3), whereas the one containing dithienyldicyanoethene derivative does not have the sensitivity to a semiconductor laser beam as required under item (1).